RMS stands for Root Mean Square. It is the effective value of an AC signal — the DC equivalent that delivers the same average power to a resistive load. For a pure sine wave, Vrms = Vpeak / √2 ≈ 0.7071 × Vpeak.

Why is mains voltage stated as 120 V or 230 V?

Those are RMS values. The actual peak voltage of a 120 V RMS supply is about 170 V, and a 230 V RMS supply peaks near 325 V. Appliances are rated at RMS because it represents real power delivery.

Does this formula work for non-sinusoidal waveforms?

No. Vrms = Vpeak / √2 applies only to pure sine waves. Square waves, triangle waves, and distorted signals have different crest factors and require waveform-specific calculations.

What is peak-to-peak voltage?

Peak-to-peak is the total swing from the negative peak to the positive peak: Vpp = 2 × Vpeak. Oscilloscopes typically display peak-to-peak values.

What is the crest factor for a sine wave?

The crest factor is Vpeak / Vrms = √2 ≈ 1.4142. It describes how much higher the peak is compared to the RMS value.

AC RMS Calculator

Enter a peak (or RMS) AC value to instantly convert between peak, RMS, and peak-to-peak voltage or current.

Input

Quantity

Known value type

Peak Voltage (V)

Quick Presets

Results

Enter a value and click Calculate.

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Summary

This AC RMS Calculator converts between peak, RMS, and peak-to-peak values for sinusoidal AC voltage or current. It uses the standard formula Vrms = Vpeak / √2 (crest factor √2 ≈ 1.4142), which applies to pure sine waves such as mains electricity and typical signal generators. Enter any one value and all three representations are computed instantly.

How it works

Select whether you are entering a Voltage or Current value.
Choose the input type: Peak or RMS.
Type your value in the input field.
The calculator applies Vrms = Vpeak / √2 (or rearranges for the reverse).
Results for RMS, Peak, and Peak-to-Peak are shown instantly.

Use cases

Convert mains supply voltage (e.g. 120 V or 230 V RMS) to its peak value.
Find the RMS current through a resistor driven by a peak AC source.
Verify oscilloscope peak readings against datasheet RMS ratings.
Design power electronics where both peak and RMS values are required.
Check transformer winding voltages during AC circuit analysis.
Understand the relationship between peak and effective (RMS) power delivery.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu